Every multi-dimensional measure can be projected onto one dimension. The question is whether it still retains useful discriminating power at that point.
The whole argument in favor of a g factor in intelligence is that when you measure different kinds of intelligence (verbal, analytical etc.) the numbers you get seem to be a function of a single dominant factor. (That's the argument, I'm not saying whether or not I agree with it.)
The whole argument in favor of a g factor in intelligence is that when you measure different kinds of intelligence (verbal, analytical etc.) the numbers you get seem to be a function of a single dominant factor. (That's the argument, I'm not saying whether or not I agree with it.)